Tree trunk shear

ABSTRACT

A tree trunk shear includes two opposed blades each pivotally mounted by two links to a U-shaped frame. Hydraulic power means is operative on the links adjacent the base of the U-shape frame to draw cutting edges of the blades toward each other and toward the base to slice through any tree trunks or other fibrous material positioned between the open arms of the U-shape frame. The relatively thin blades are held in position by the presence of heavy blade frames around the outer periphery of the blades except along their cutting edges.

O United States Patent [191 Barwise Oct. 30, 1973 TREE TRUNK SHEARPrimary Examiner-Gerald A. Dost [76] Inventor: Robert D. Bar-wise, Route2, Braddock et Q9KZ2B9XY1MPQ 5.5199 [22] Filed: Dec. 10,1971 ABSTRACT[2]] Appl, No; 206,675 A tree trunk shear includes two opposed bladeseach pivotally mounted by two links to a U-shaped frame. Hydraulic powermeans is operative on the links adja- [22] :J.S.CCEL 144/34 E, 144/309AC cent the base of the U shape frame to draw cutting .na. dg of theblades toward h other and toward the 1 e of Seflrc E, 3 D base to slicethrough y tree trunks or other fibrous material positioned between theopen arms of the U- [56] References cued shape frame. The relativelythin blades are held in po- UNITED STATES PATENTS sition by the presenceof heavy blade frames around 3,527,272 9/1970 Hamilton 144/3 D the outerperiphery of the blades except along their 3,613,752 10/1971 Davis144/34 E cutting edges. 3,183,954 5/1965 Larson 144/34 E 3,270,7879/1966 Rehnstrom 144/34 E 6 Claims, 4 Drawing Figures PMFNIEUum 30 msSHEET 10F 2 Jrrmzwsxs PATENTEflnmso ma 3. 768,528

I Y SHEET 20F 2 INVEUTOR ROSE RT .D. BAka/lsz FIG: 4 8) M WM Arroxwsr:

TREE TRUNK SHEAR BACKGROUND OF THE INVENTION This invention relates toan apparatus for cutting tree trunks, logs, and the like by the slicingaction of opposed parallel approximately aligned blades movingsimultaneously toward each other and toward and through a backup plateagainst which tree trunks or the like are positioned.

It is well known to use shear blades on fixed pivots to cut tree trunks.See, for example, FIGS. 1 and 6 of U. S. Pat. No. 3,468,352, and FIG.3of U. S. Pat. No. 3,l22,l84. Such structures act by exerting acompressive shearing force on the wood to sever it. This action socrushes the portions of the tree trunks or logs adjacent the cut thatthe resulting logs not only are not suitable to be sawn into boards, butare so multilated that the fibers therefrom are not even acceptable topole and post plants or to pulp mills that grind their wood.

Typically this kind of compressive shearing action consistently resultsin fiber pulling from the ends of the sheared portions for a total of atleast six inches, that is, about three inches on either side of thesheared butt. A straight shearing action about a fixed pivot, such asdisclosed in U. S. Pat. No. 3,468,352 for example, also tends to forcethe tree trunk out from between the shear blades rather than to hold itin.

Other patents which show compressive shearing and so cause excessivecrushing and fiber pulling damage are U. S. Pat. Nos. 3,509,922 and3,503,429. Because of the use of compressive force in order toaccomplish shearing in all of the patents mentioned above, it isessential that an extremely heavy shear blade be used. This blade,necessarily displacing wide areas of the tree trunk as it movestherethrough, necessarily severely increases the amount of fiber that isdamaged. Also, use of such thick blades necessarily increases the amountof power needed to force those blades through the tree trunk. Thisexcessive use of power necessitates use of large and heavy increase inframes to carry the shear blades and transmit power thereto.

Slicing action has been attempted with shear blades in the past. See U.S. Pat. Nos. 3,527,272 and 3,270,787. The structures in these patentsstill rely primarily on a pushing action, however. As shown in each ofthose patents, substantially the same massive blade size is-required toachieve effective shearing action as in the use of blades directlypivoted to a rigid frame. See the cutting member 2 in FIGS. 1 and 3 inPat. No. 3,270,787 and cutting member 83 in FIG. 2 of U.S. Pat. No.3,527,272. Also note the heavy base or frame constructions shown,particularly in FIG. 1 of U.S. Pat. No.

3,270,787. Typically, blades over one-half inch in thickness areutilized to achieve effective shearing actions in these structures ofthe prior art.

At the time the tree trunk shear of the present invention was beingdeveloped, there was a need to reduce fiber damage, and crushing andsplitting of the tree trunk at the point of the shearingaction. Theweight of the shear blades and of the supporting framework needed to besubstantially lightened so that the tree shear could be effectivelymounted on and handled by small skidders, tractors, front end loadersand knuckle brooms, etc. The power requirements had to be reducedsufficiently so that the horsepower available on the majority ofexisting mobile hydraulic systems could operate the shear.

All of these criteria can be met by circle saws and chain saws, but asawing action necessarily results in the production of sawdust which isa substantial pollutant at tree trunk processing sites. Where theattributes of the tree trunk shears of the prior art are not acceptable,saw are used today; and a major reason for the development of the treetrunk shear of the present invention is to obtain the advantages of thelightness in weight, low power requirements, and flexibility of thesawing operations without the pollutant and other disadvantagesattendant on the use of saws. So important is the pollution problemgrowing out of production of sawdust that, at the time of the writing ofthis specification, the Canadian government has set a limited timeperiod by the end of which, logging operations must shift from sawing toshearing methods.

Other disadvantages attendant on the use of saws include excessive downtime occasioned by the need to sharpen saws. Four and one-half to fivehours of actual production time is all that can be expected from one 8hour shift when saws are used. Saws are many times more hazardous to usethan shears under the best of conditions, and are even moreunsatisfactory in foul weather and night operations. This necessitatesmuch higher insurance expense.

Against this background the tree trunk shear of the present inventionwas developed.

SUMMARY OF THE INVENTION In order to utilize a thinner blade, the treetrunk shear of the present invention utilizes a slicing and drawingaction in which the blade acts primarily in tension rather than incompression. In order to keep the thinner blade from buckling orcollapsing, a heavy, rigid blade support frame is utilized around theouter periphery of each blade except along the cutting edge of thatblade. This is similar to holding a sheet of paper between the thumb andforefinger of each hand, maintaining the paper in tension and thendrawing it across an object to be cut. Accidental cuts received frompaper acting with a true slicing action in tension rather than with acompressive action have been commonly experienced by almost everyone. Inorder to utilize this slicing action, an open U-shape frame is utilizedwith the tree trunks or logs or the like to be cut positioned against abackup plate in the base section of the U-- shape frame and between theoutwardly extending, spaced apart arms of the U.

It is desirable that the shear blades tend to force the wood being cutback into the backup plate of the base section of the U rather than totend to force the trees outwardly from the base as is the casewhen twoshear blades are pivoted from a single point. This can be accomplishedby utilizing shear blades in compression as seen, for example, in FIG. 3of U. S. Pat. No. 3,122,184; but this necessitates using extremely heavyblades 'to accomplish the compressive shearing action. Thiscan also beaccomplished, as in the present invention, by causing the slicing actionto take place in direction to hold and to force the tree trunk or logtowards the base of the U-shaped frame.

In the form of the invention as shown, the U-shape frame includes twoparallel spaced apart plates with the shear blades each pivotallymounted therebetween to a pair of links, the links and blades movingbetween the plates from a position where the entire blade is between theplates and the throat of the U is entirely open to receive the trees orthe like, to a position where the blades are in contact with each otherafter having cut through whatever trees were positioned against the basesection at the base of the U-shape frame. One set of links is mountedwithin the base section and this set, in the device as shown, is poweredin direction to cause the blades to move toward and away from each otherby operating arms extending integrally outwardly from these links and bya double acting extensible and retractible power source, such as ahydraulic cylinderpiston motor.

In the form of the invention as shown, an upright stanchion is attachedto the U-shape frame at the base section and suitable grapples areprovided on'the stantion for holding the tree trunk to be sheared in anupright position during and after the shearing operation. Suitable beamsand hydraulic actuators or the like are provided for the mounting of thedevice on any suitable vehicle, such, for example, as a tractor. It isto be understood, however, that the principles of the invention wouldapply equally well were the U-shape frame to be situated at 90 from thatillustrated with the arms extending straight up and the base sectionlying at the bottom. In this form, the invention will be particularlyuseful in cutting logs to desired lengths, for example.

In the drasings:

FIG. 1 is a perspective view of a tree trunkshear made according to oneform of the invention;

FIG. 2 is an enlarged top plan view of the device of FIG. 1 with partsbroken away and parts in section;

FIG. 3 is a further enlarged horizontal sectional view taken on the line3-3 in FIG. 1; and

FIG. 4 is a vertical sectional view taken generally on the line 4-4 inFIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT A tree trunk shear includes aU-shape frame 12 to which are welded suitable mounting brackets 14, 14.Mounting beams 15 and hydraulic actuators 16 extend from a suitablevehicle (not shown) such as a tractor having a source of hydraulic fluidunder pressure (not shown).

The U-shape frame 12 includes spaced apart open arms l8, l8 integralwith and extending outwardly from a base section 20.

An upright stanchion 22 extends integrally from the base section 20, andsuitable grapple arms indicated generally at 24 are operably associatedwith the stanchion to be in position to grasp a tree trunk, or the like,the lower portion of which has been encompassed 'by the U-shape framebetween the arms 18, 18. These grapple arms may be hydraulically orotherwise operated in any usual or preferred manner, forming no part ofthe present invention.

The U-shape frame 12 is made up of an upper plate 26 and a lower plate28 fixedly positioned in spaced relationship to each other by integraledge strips 30, 32 and 34. An upper backup plate 36 is integral with andwelded to upper plate 26 to form part of the base section 20, and lowerbackup plate 38 is integral with and welded to lower plate 28 of theU-shape frame 12 also to form part of the base section 20. The upperbackup plate and lower backup plate are spaced from each othersufficiently to allow passage of shear blades 40, 40.

These blades 40 are each part of one of the blade assemblies 42, 42.Other parts of each of those assemblies include rigid, relatively stiff,blade frames 44, 44 which are securely fastened as at 46 around the edgeportion of each of the blades to stiffen the blades and to tend hold itin tension. While a riveted fastening is shown, it is to be understoodthat other means for rendering the blade frames integral with theblades, such as welding, could also be used.

Guide toggle links 48, 48 are pivotally mounted as at 50 to the arms 18,18 of the U-shape frame 12; and are pivotally mounted as at 52 to theouter periphery of the blade frames 44, 44. Draw toggle links 54, 54 arepivotally mounted to the base section 20 of the U-shape frame 12 as at56 and are pivotally mounted to the innermost edges of the blade frames44, 44, adjacent cutting edges 72 as at 58. These draw toggle linksinclude operating arms 60, 60, each of which is pivotally mounted as at64 to an extendible and retractible power means illustrated as ahydraulic cylinder-piston motor 62.

As shown, the hydraulic motor 62 can be caused to extend by introductionof hydraulic fluid under pressure through hydraulic conduit 66 andevacuation of such fluid through hydraulic conduit 68 to and from asource of such fluid (not shown). When the flow in such conduits isreversed, the hydraulic motor will be caused to retract in length.

OPERATION The operation will be described in terms of felling a tree byshearing its tree trunk 70, but it is to be understood that the relativeoperation of the parts will be the same regardless of the positioning ofthe U-shape frame with respect to the horizontal, as long as therelative positioning of this frame with respect to the logs, limbs, treetrunks or other elongated fibrous material remains substantially asexplained below.

With the shear blade assemblies 42, 42 positioned as seen in dottedlines in FIG. 3, the mounting beams 15 and hydraulic actuators 16 willbe utilized to position the U-shape frame 12 in encompassingrelationship to tree trunk 70 as seen in FIG. 2. Grapple arms 24 areengaged with an upper portion of the trunk. Hydraulic fluid underpressure is then introduced through hydraulic conduit 66 to cause powermeans 62 to be elongated. This forces operating arms 60, 60 of the drawtoggle links 54, 54 to move toward each other, thus causing these drawtoggle links, acting through blade frames 44, to move the shear blades40, 40 from the position as seen in dotted lines in FIG. 3, through theposi tion disclosed in FIG.2, and to the position as shown in FIG. 1 andas shown in full lines in FIG. 3. Sharpened cutting edges 72, 72 of theblades 40 move in substantially parallel relation toward each other witha slicing action as they move simultaneously toward the base section 20of the U-shape frame. As soon as they encounter the tree trunk 70, theybegin a slicing action on the fibers of the trunk, this action tendingto draw the trunk more firmly into contact with the upper and lowerbackup plates 36 and 38.

This action is to be likened to the drawing of a knife edge over the endof the finger. A very substantial pressure can be withstood by the fleshof the finger, for example, when a knife blade is simply pressed againstit and without any lateral movement being imparted to it. A slicingmovement, however, combined with the inward pressure in exactly the samemanner as the blades 40 move with respect to the tree trunk, instantlycauses a slicing of the finger. The parallelism of movement of thecutting edges 72, 72 is insured by the guide toggle links 48, 48,pivoted, as they are, to the arms l8, 18 of the U-shape frame 12 and tothe rigid blade frames 44 of the shear blade assemblies 42. I

The rigidity of the blade frames 44 is such that the tendency of theblades 40 to buckle due to their component of motion toward the heart ofthe tree 70 will be overcome by forces exerted on the blades in tensionaction effectively between an outer end portion 74 of each blade frameand an inner end portion 76 thereof. As set out above, this iscomparable to the tensioning of a piece of paper and using its edgeportion to slice or cut. Utilizing these rigid outer blade frames, it isobvious. that the thickness of the blade is no longer the dominantdetermining factor in obtaining the rigidity necessary to shear andslice as the blade is drawn (not pushed) through the wood, in accordancewith the teaching of the invention.

Stated differently, the cutting edge 72 of the shear blades 40 aresomething like strings which are held between the forefingers and thumbsof each hand, and are similar to the string-like saws used by surgeonsin cutting bone and other material inside of the body, for example, inbrain surgery. The difference is that the cutting edges 72, 72 rely on aslicing action to separate the fiber while the string-like saws used bydoctors rely on the abrasive qualityof the string to cut. in any case,the string-like saw has absolutely no strength in compression. In fact,it hangs like any other string when supported at one point. Whensupported at two points, however, on the doctors forefingers, forexample, and when moved longitudinally, the material with which the sawis in contact will be sawed apart. The blades 40, moving only indirection toward the frame and in direction toward each other, and, mostimportantly, being pulled or drawn like the string-like saw, need verylittle strength in compression, and will not buckle because the forcesexerted keep the blades in tension.

As the blades proceed deeper into the heart of the tree trunk being cut,the forces of tension are greatest along the portion of the blade 72just emerging from the tree trunk. The forces are least at the portionof the blade 72 which has just entered the tree trunk. It is to beunderstood, therefore, that the necessity for'the heavy, rigid bladeframe at position beyond point 52 where the guide toggle link issupported on the blade frame is no where near as great as around therest of the periphery of the blade. In fact, in some instances, it ispossible to eliminate this blade frame from the point 52 around towardsthe outer tip of the blade 40.

As best seen in FIG. 1, the cutting blades 40, 40 as shown, are not inexact horizontal alignment with each other, and actually the cuttingedges 72, 72 overlap slightly when the blade assemblies 42, 42 havereached the inward limit of their travel and tree trunk 70 is completelysheared. it is to be understood, however, that a tree trunk shear of theinvention would operate entirely satisfactorily if the blades were inthe same plane and the cutting edges did meet.

After the tree trunk has been severed, the hydraulic actuators 16 can beutilized to lift the entire tree trunk shear 10, the grapple arms 24will maintain the tree trunk in an upright position and in contact withthe upper backup plate 36 while the severed tree trunk is beingtransported with the tree trunk shear toward a desired location for useof the tree trunk. After the grapple arms have been disengaged from thetree trunk, hydraulic motor 62 will be activated to return the shearblade assembles 42 to position as seen in dotted lines in FIG. 3, andthe tree trunk shear 10 can be moved in on another tree trunk to besevered.

While the action of the shear has been described in connection with asingle tree trunk, it is to be understood that it can be used to bunchseveral trees and to sever them.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A shear for severing elongated fibrous material including a shearsupport frame having a base section; and spaced apart open armsextending outwardly from the base section; a pair of draw toggle linkspivotally mounted with respect to said section; a pair of shear bladeassemblies, each assembly including a flat shear blade of area more thansufficient to overlie one-half of the maximum area to be sheared, eachblade having a sharp cutting edge, and each assembly further including arelatively stiff blade frame integrally connected with said blade aroundthe edges thereof except said cutting edge; each of said blade framesbeing'pivotally mounted to one of said draw toggle links at positionadjacent that first end of the cutting edge of its associated bladewhich is adjacent the base section; the relation of the toggle links andthe pivotal mountings of those links to the shear support frame and tothe blade assemblies being such that each assembly can move between afirst position wherein said first end of each blade cutting edge is inspaced apart relation to said first end of the other blade cutting edgeat a predetermined maximum distance away from the base section and asecond position wherein each such first end of the cutting edge is inadjacent relation to the other such edge at a lesser distance from saidbase section; means cooperating between each blade frame and an adjacentshear support frame arm to cause said cutting edges to remain in substantially parallel relation to each-other as said blade assemblies movefrom said first'to said second position; and power means operative onsaid first ends of said blade assemblies to move said assemblies fromsaid first to said second position. A

2. A shear for severing elongated fibrousmaterial in cluding a shearsupport frame having a base section; a pair of draw toggle linkspivotally mounted with respect to said section; a pair of guide togglelinks pivotally mounted with respect to said shear support frame; a pairof shear blade assemblies, each assembly including a flat shear blade ofarea more than sufficient to overlie one-half of the maximum area tobesheared, each blade having a sharpened ,cutting edge, and each assemblyfurther including a rigid, relatively stiff, blade frame integrallyconnected with said blade around all edges thereof except said cuttingedge; each of said blade frames being pivotally mounted to one of saiddraw toggle links at position adjacent that first end of the cuttingedge of its associated blade which is adjacent the base section of theshear support frame and being pivotally mounted to one of said guidetoggle links; the relationship of the toggle links and the pivotalmountings of those links to the shear support frame and to the bladeassemblies being such that each assembly can move between a firstposition wherein each blade cutting edge is in spaced apart relation tothe other blade cutting edge at a predetermined maximum distance awayfrom said base section and a second position wherein each blade cuttingedge is in adjacent relation to the other edge at a lesser distance fromsaid base section; and power means to cause said draw toggle links tomove said blade assemblies from said first to said second position.

3. The combination of claim 2 wherein said shear support frame isconstituted as two parallel, integrally connected, spaced apart platesand said toggle links and blade assemblies are pivotally mounted betweensaid plates.

4. The combination of claim 3 wherein said shear support frame isU-shaped and includes a pair of spaced apart arms extending outwardlyfrom said base section and wherein each of said guide toggle links ismounted in a separate one of said arms.

5. A shear for severing elongated fibrous material including a shearsupport frame having a base section; a pair of draw toggle linkspivotally mounted with respect to said section; a pair of guide togglelinks pivotally mounted with respect to said shear support frame; a pairof shear blade assemblies, each assembly including a flat shear blade ofarea more than sufficient to overlie one-half of the maximum area to besheared, each blade having a sharpened cutting edge, and each asmountedto one of said guide toggle links; the relationship of the toggle linksand the pivotal mountings of those links to the shear support frame andto the blade assemblies being such that each assembly can move between afirst position wherein each blade cutting edge is in spaced apartrelation to the other blade cutting edge at a predetermined maximumdistance away from said base section and a second position wherein eachblade cutting edge is in adjacent relation to the other such edge at alesser distance from said base section; and power means to cause saiddraw toggle links to move said blade assemblies from said first to saidsecond position; said shear support frame being constituted as twoparallel, integrally connected, spaced apart plates each of which isU-shaped and includes a pair of spaced apart arms extending outwardlyfrom said base section, said toggle links and said blade assembliesbeing pivotally mounted between said plates, each of said guide togglelinks being so mounted in a separate one of said arms; said base sectionhaving an upper backup plate above and a lower backup plate below theblades, said blades being situated in facing, material receivingrelation to the open area between the spaced apart arms of the shearsupport frame; there being an operating arm extending outwardly from andoperably associated with each of the draw toggle links; said power meansbeing operative on outer ends of said arms to rotate said draw togglelinks.

6. The combination of claim 5 wherein said power means is constituted asa cylinder-piston fluid motor.

73 3 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,768,528 Dated c er 30, 1973 Robert D. Barwise Inventor(s) It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 6, cancel "saw" and insert saws-.

. Column 3, line .26, cancel "drasings" and insert -drawings-.

Column 5, line l0, cancel "action' and insert- -acting-.

Signed and oealed this 9th day of April 19714..

Attest:

EDWARD. M.FLETGHER,JR. C. I IARSHALL DAMN Attesting Officer I 7Commissioner of Patents

1. A shear for severing elongated fibrous material including a shearsupport frame having a base section; and spaced apart open armsextending outwardly from the base section; a pair of draw toggle linkspivotally mounted with respect to said section; a pair of shear bladeassemblies, each assembly including a flat shear blade of area more thansufficient to overlie one-half of the maximum area to be sheared, eachblade having a sharp cutting edge, and each assembly further including arelatively stiff blade frame integrally connected with said blade aroundthe edges thereof except said cutting edge; each of said blade framesbeing pivotally mounted to one of said draw toggle links at positionadjacent that first end of the cutting edge of its associated bladewhich is adjacent the base section; the relation of the toggle links andthe pivotal mountings of those links to the shear support frame and tothe blade assemblies being such that each assembly can move between afirst position wherein said first end of each blade cutting edge is inspaced apart rElation to said first end of the other blade cutting edgeat a predetermined maximum distance away from the base section and asecond position wherein each such first end of the cutting edge is inadjacent relation to the other such edge at a lesser distance from saidbase section; means cooperating between each blade frame and an adjacentshear support frame arm to cause said cutting edges to remain insubstantially parallel relation to each other as said blade assembliesmove from said first to said second position; and power means operativeon said first ends of said blade assemblies to move said assemblies fromsaid first to said second position.
 2. A shear for severing elongatedfibrous material including a shear support frame having a base section;a pair of draw toggle links pivotally mounted with respect to saidsection; a pair of guide toggle links pivotally mounted with respect tosaid shear support frame; a pair of shear blade assemblies, eachassembly including a flat shear blade of area more than sufficient tooverlie one-half of the maximum area to be sheared, each blade having asharpened cutting edge, and each assembly further including a rigid,relatively stiff, blade frame integrally connected with said bladearound all edges thereof except said cutting edge; each of said bladeframes being pivotally mounted to one of said draw toggle links atposition adjacent that first end of the cutting edge of its associatedblade which is adjacent the base section of the shear support frame andbeing pivotally mounted to one of said guide toggle links; therelationship of the toggle links and the pivotal mountings of thoselinks to the shear support frame and to the blade assemblies being suchthat each assembly can move between a first position wherein each bladecutting edge is in spaced apart relation to the other blade cutting edgeat a predetermined maximum distance away from said base section and asecond position wherein each blade cutting edge is in adjacent relationto the other edge at a lesser distance from said base section; and powermeans to cause said draw toggle links to move said blade assemblies fromsaid first to said second position.
 3. The combination of claim 2wherein said shear support frame is constituted as two parallel,integrally connected, spaced apart plates and said toggle links andblade assemblies are pivotally mounted between said plates.
 4. Thecombination of claim 3 wherein said shear support frame is U-shaped andincludes a pair of spaced apart arms extending outwardly from said basesection and wherein each of said guide toggle links is mounted in aseparate one of said arms.
 5. A shear for severing elongated fibrousmaterial including a shear support frame having a base section; a pairof draw toggle links pivotally mounted with respect to said section; apair of guide toggle links pivotally mounted with respect to said shearsupport frame; a pair of shear blade assemblies, each assembly includinga flat shear blade of area more than sufficient to overlie one-half ofthe maximum area to be sheared, each blade having a sharpened cuttingedge, and each assembly further including a rigid, relatively stiff,blade frame integrally connected with said blade around all edgesthereof except said cutting edge; each of said blade frames beingpivotally mounted to one of said draw toggle links at position adjacentone end of the cutting edge of its associated blade and being pivotallymounted to one of said guide toggle links; the relationship of thetoggle links and the pivotal mountings of those links to the shearsupport frame and to the blade assemblies being such that each assemblycan move between a first position wherein each blade cutting edge is inspaced apart relation to the other blade cutting edge at a predeterminedmaximum distance away from said base section and a second positionwherein each blade cutting edge is in adjacent relation to the othersuch edge at a lesser distance from said base section; and power Meansto cause said draw toggle links to move said blade assemblies from saidfirst to said second position; said shear support frame beingconstituted as two parallel, integrally connected, spaced apart plateseach of which is U-shaped and includes a pair of spaced apart armsextending outwardly from said base section, said toggle links and saidblade assemblies being pivotally mounted between said plates, each ofsaid guide toggle links being so mounted in a separate one of said arms;said base section having an upper backup plate above and a lower backupplate below the blades, said blades being situated in facing, materialreceiving relation to the open area between the spaced apart arms of theshear support frame; there being an operating arm extending outwardlyfrom and operably associated with each of the draw toggle links; saidpower means being operative on outer ends of said arms to rotate saiddraw toggle links.
 6. The combination of claim 5 wherein said powermeans is constituted as a cylinder-piston fluid motor.